TPG Contributor “Vic Vector” is an air traffic controller at a major ATC facility in the United States. In this installment of our “Insider Series,” he explains the basic principles of separating aircraft and how controllers keep planes apart — despite not being able to see them.
In my very first installment of the Insider Series, I covered the different types of facilities in which air traffic controllers work and how a flight spends the majority of its airborne time under the guidance of controllers that use radar. Fortunately, radar coverage in the contiguous United States is excellent, so there are very few places planes can go in American airspace where our radar can’t reach.
However, as radar tracking requires ground stations and line-of-sight, almost all of the ocean is completely devoid of radar coverage — which begs the question: How do air traffic controllers keep airplanes separated from each other during transoceanic flights?
The answer is a method called “non-radar separation.” It’s one of the most fundamental types of enroute air traffic control and is also one of the first things taught at the ATC academy — and it occurs far from airports.
There are three basic ways to separate aircraft, pertaining to the three dimensions in which aircraft operate — vertical, lateral and longitudinal.
Vertical separation: Two airplanes at two different altitudes are always separated.
Lateral separation: Two airplanes on two parallel routes that never intersect will maintain separation.
Longitudinal separation: Two airplanes following the same route at the same altitude are ensured separation when they maintain exclusive speeds, much like one car following another on a highway.
ATC always separates aircraft via a combination of these three types of separation, with or without radar. However, their application in a non-radar environment becomes much less precise — but in a way, much more crucial.
There are several groups of airways — or “tracks,” as they’re called in traffic control — that pass over the ocean and are grouped like multi-lane interstates. For the sake of simplicity, let’s take a look at one of the most popular and heavily trafficked group of oceanic tracks, known as the North Atlantic Tracks — or the NAT Tracks— which exist between North America and Europe, in either direction.
Flights leave North America for Europe in the late afternoon or evening, arriving early in the morning. Flights leave Europe in the late morning or early afternoon, and due to the time change, arrive in North America only a few hours later. Based on prevailing winds, the actual location of the NAT Tracks along these transoceanic routes change twice a day in order to minimize headwinds, maximize tailwinds and enable passengers to make flight connections.
Prior to departure, airline dispatch personnel responsible for these transoceanic routes check the current position of the NAT Tracks and take into account each flight destination, as well as the aircraft’s type, weight and planned speed. They then submit a request to enter a specific track at a certain time. Their requests are submitted to one of two air traffic control centers — Gander Center in Newfoundland, Canada or Shanwick Center in Ayrshire, Scotland — which are responsible for compiling and organizing these requests in order to assign standard separation of aircraft along the tracks.
However, ATC can’t use radar to track the position of aircraft along these transoceanic routes — so how do they manage to maintain safe separation between aircraft?
Check out this video from NATS.aero to see how these NAT Tracks appear in airspace:
As you can see, there are multiple NAT Tracks. Each has its own entry and exit points and each has a lateral separation of at least 50 miles. These tracks are generally usable between 29,000-41,000 feet. Using the standard enroute vertical separation of 1,000 feet, this spacing provides 13 different altitude strata per track.
While standard en route longitudinal separation in a radar environment is only five miles, the imprecision because of the lack of radar creates the need to keep aircraft on the same route and at the same altitude separated by 10 minutes of flying time. Based on the typical cruising speed of your average airliner, 10 minutes equates to around 80-90 miles of longitudinal separation.
While transoceanic radar coverage is sparse, communication is still required, usually by means of long-range, high-frequency radio or satellite data link. Along each of the NAT Tracks, there are several mandatory reporting points at which pilots must contact one of the oceanic ATC centers (Gander or Shanwick) and check-in to report their position and their estimated time at the next fix on their route. ATC uses these position reports to ensure the assigned speeds of all airborne craft along a given track are working, keeping them at least 10 minutes apart and making adjustments if necessary.
Like radar controllers, oceanic controllers must transpose data from a two-dimensional image into a three-dimensional mental model, maintaining complete situational awareness to ensure the separation of aircraft traversing the tracks — even in the case of pilot deviations from their flight course, altitude or speed due to bad weather or a mechanical problem. When a flight eventually reenters an area of radar coverage, then radar is once again used to guide the plane to a safe landing.
Keep in mind this is but one example of the numerous oceanic route structures that exist over every ocean across the entire world. In the US, the New York Center in Ronkonkoma, New York controls our portion of the Atlantic Ocean, while Oakland Center in Fremont, California is responsible for our share of the Pacific.
Like all other controllers, oceanic controllers play an important role in managing the safe and expeditious flow of traffic through their portion of the world airspace system. With each of us playing our part, together we can take you quite literally to the other side of the world and back.